The present invention relates to a diagnostic system for a motor vehicle.
Recently, a motor vehicle has been equipped with an electronic control system for controlling various components of an engine, such as fuel injectors, thereby improving driveability, exhaust gas emission, fuel consumption and engine power. The electronic control system controls the components based on information represented by output signals from various sensors for detecting engine operating conditions. If malfunctions of components and sensors occur, the engine does not properly operate.
However, because of complexity of the electronic control system, it is difficult to immediately find out the trouble. Accordingly, a diagnostic device for easily checking the electronic control system should be provided in an auto shop.
Japanese Patent Application Laid Open 59-61740 discloses a diagnostic system where signaling lamps provided on the vehicle are lighted or flashed when abnormalities occur in sensors and actuators such as injectors. However, the actual conditions of the defective sensors and actuators cannot be represented by the lamps.
Japanese Patent Application Laid-Open 58-12848 discloses a diagnostic system in which an exclusive checking device is provided for measuring the pulse duration of fuel injection and engine speed, and for checking whether the idling speed is normal. The checking device is provided for diagnosing only a designated specific type of a motor vehicle.
FIG. 5 shows a recently proposed diagnostic system which comprises a diagnostic device 102 and one of several memory cartridges 103 detachably attached to the device 102. The memory cartridge 103 has a memory such as a ROM for storing diagnosis programs and fixed data for the type and the model year of a motor vehicle 100. The various cartridges 103 for all vehicle types and models are provided and a cartridge for the presented vehicle is selected and attached to the diagnosis device 102. Two-way communication between the cartridge 103 and an electronic control unit 101 on the vehicle 100 is performed for diagnosing the electronic control unit 101. Thus, various types of vehicles can be diagnosed by the diagnostic device
The electronic control unit 101 has a self-diagnosis function to store trouble data in a memory when troubles occur in equipment such as sensors and actuators.
However, addresses for storing the trouble data in the memory and the conversion rate for converting data to physical values differ with different types and models of vehicles.
Additionally, if the electronic control unit 101 is improved without changing the model of the vehicle, or the diagnosis program is changed in accordance with the improvement, or diagnosis items increase due to the addition of sensors and actuators, the addresses for storing data and conversion rate may be changed. Thus, a diagnostician must consult a manual to find a corresponding cartridge for the particular diagnosis program and vehicle type. Consequently, a considerable time must be spent for the diagnosis. Furthermore, a plurality of cartridges must be provided for every vehicle type and model, resulting in an increase in the cost.